Hitherto, as the charge generating material for an electrophotographic photoreceptor having a sensitivity to visible light and near infrared light, many materials such as condensed aromatic pigments, pyrylium dyes, perylene pigments, squarylium pigments, bisazo pigments, trisazo pigments, phthalocyanine pigments, etc., are known and various proposals have been made.
On the perylene pigments, various proposals have been made in JP-A-57-176047 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-59-59686, JP-A-63-180956, JP-A-63-291061, JP-A-63-243947, JP-A-63-243946, JP-A-2-37356, JP-A-2-228670, JP-A-2-228671, JP-A-3-24059, and U.S. Pat. Nos. 4,587,189, 3,992,205, 4,419,427, 5,019,473, etc.
Also, as a method of forming a charge generating layer for an organic photosensitive material, a vapor deposition method and a coating method are generally known but the coating method is more advantageous for the production in the view points of not requiring a complicated evacuating apparatus, etc., and of easily controlling the film thickness.
A perylene pigment is an excellent charge generating material but there is a problem that when a charge generating layer composed of the perylene pigment is formed by a coating method, the sensitivity thereof becomes lower than the case of forming the charge generating layer of the perylene pigment by a vapor deposition method.
For improving this point, U.S. Pat. No. 5,019,473 described above proposes that a perylene pigment is mechanically ground and the finely powdered perylene pigment is used in a coating liquid for forming a charge generating layer. However, the coating liquid prepared by the method can form an electrophotographic photoreceptor initially showing an excellent sensitivity but since the electrophotographic photoreceptor is desensitized with the passage of time, the method is unsuitable for the case of forming the charge generating layer by a coating method.